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30 UMG70XV3-4EN 12.01.2009
5 Selection of the Measuring Point
5 Selection of the Measuring Point
The correct selection of the measuring point is crucial for achieving reliable measure-
ment results and a high measurement accuracy. A measurement must take place on a
pipe in which
• the ultrasound propagates with sufficiently high amplitude
• the flow profile is fully developed (see section 5.2)
• the influence of noise is sufficiently low (see section 5.3)
The correct selection of the measuring point and thus, the correct transducer positioning
guarantees that the sound signal will be received under optimum conditions and evaluat-
ed correctly.
Because of the variety of applications and the different factors influencing the measure-
ment, there can be no standard solution for the transducer positioning. The correct posi-
tion of the transducers will be influenced by the following factors:
• diameter, material, lining, wall thickness and form of the pipe
• medium
Avoid locations where deposits are building in the pipe. The ambient temperature at the
measuring point must be within the operating temperature range of the transducers.
Select the location of the flowmeter within cable reach of the measuring point. Make sure
that the ambient temperature at the location is within the operating temperature range of
the flowmeter (see annex A, section Technical Data).
If the measuring point is within an explosive atmosphere, the danger zone and gases
which may be present have to be determined. The transducers and the flowmeter have
to be appropriate for these conditions.
5.1 Acoustic Penetration
Observe the safety instructions in chapter 2.
The pipe must be acoustically penetratable at the measuring point. The acoustic penetra-
tion is reached when pipe and medium do not attenuate the sound signal so strongly that
it is completely absorbed before reaching the second transducer.
The attenuation of pipe and medium depends on:
• kinematic viscosity of the medium
• the proportion of liquids and solids in the medium
• deposits on the inner pipe wall
• pipe material
Note!
Avoid measuring points in the vicinity of deformations and defects of
the pipe and in the vicinity of welds.